Epidemiological study designs by Moonga Given - University of Zambia - Public Health-unza

Epidemiological study designs Moonga Given Department of Public Health School of Medicine-University of Zambia 14th October 2015 DPH 6024 Learning objectives By the end of this session, students should be able to: – Provide classification and discuss different types of epidemiological study design What is a Study Design? A strategy used for the selection of respondents, the data gathering techniques to be used and the data analysis to be done. It varies according to the research problem identified and research questions developed. Epidemiological Methods • Classifications by: – Approach to data collection – Goal – Timing and directionality – Unit of analysis Definition of Epidemiology “Epidemiology is the study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems.” - Last’s Dictionary of Epidemiology Study Designs Distribution  Descriptive studies Determinants  Analytic studies Distinction: Descriptive from Analytical study designs In terms of research question: Descriptive studies Aim to describe only, without an explicit interest in cause-and-effect relationships (no causal orientation). Example; Is overcrowding associated with TB? Analytical studies Aim to demonstrate causal links (causal orientation). Example; Is smoking causing lung cancer? Distinction: Descriptive from Analytical study designs In terms of hypothesis generation and testing: Descriptive studies Used to generate hypothesis. Analytical studies Used to test hypothesis. Distinction: Descriptive from Analytical study designs In terms of comparison group: Descriptive studies No comparison group. Analytical studies Presence of comparison group. Types of Epidemiological Study Designs Descriptive Case reports Case series Cross-sectional studies (Surveys) Analytical Cohort studies Case control studies Experimental Studies (Randomized Controlled Trials) Ecologic studies* (A way of thinking, not a type of study) Cross- sectional Case-control Trials Intervention randomly assigned Individually randomised Cluster randomised Observational Experimental Studies Main types of epidemiological studies Cohort Descriptive studies Case Report One case. New cases, new disease . For example- in clinical medicine, the characteristics of unrecognized illness may be documented as a case study - a first step towards building up a clinical picture of that illness. Case Series Multiple similar cases. An extension of case report. Cross-sectional A cross-sectional (prevalence) study is an observational study in which exposure and disease (outcome) are determined at the same point in time in a given population. The temporal relationship between exposure and disease cannot be determined. Potential for reverse causality. obesity and depression CCF and inactivity Cross-sectional "Snapshot" of well-defined population Can classify exposures and diseases at same time Captures all existing disease (serosurveys capture asymptomatic cases) Advantages: Quick, inexpensive, useful Disadvantages: Uncertain temporal relationship Survivor effect Ecological Studies Exposure and disease at aggregate (e.g., country) level Data from groups not individuals Unit of observation is a population Limitation: no individual link of E-D Types: comparison and trend Advantages: Quick, inexpensive, data available Primary Disadvantage: Aggregate association may not = individual Ecological studies A Study design ??? Rationale Availability of group-level secondary data from registries, censuses. Collection of individual-level data can be expensive and time-consuming. The interest may be in ecological determinants of morbidity and mortality rather than in determinants of illness and death in individuals. Descriptive Studies – Summary Describe patterns of occurrence Four main types: Case reports and case series Descriptive incidence studies Cross-sectional (prevalence) studies Ecologic (correlational) studies Generate hypotheses for analytic study Analytic Studies – Overview Goal: to determine the relationship between exposure and disease with validity and precision Assess determinants of disease Focus on risk factors, causes Analyze distribution of exposures and disease Used for Testing hypotheses Looking for / quantifying associations Types of Analytic Studies Experimental studies Clinical trials Community trials Observational studies Cohort studies Case-control studies Other Experimental Studies (RCT) Assign exposure randomly, follow over time and monitor for disease Types: Clinical trial Community trial “Gold standard” Ethical issues Experimental study designs/Randomized trials Clinical trials Field trials Community trials Quasi experimental studies Observational Studies Two main types: Cohort Case-control Dimensions: Directionality, timing Cohort Study Different from experiment Investigator does not dictate exposure Similar to experiment Enroll subjects on basis of exposure status Follow subjects over time and record occurrence of health event (outcome of interest) Compare rates of disease occurrence among exposed and unexposed groups of persons Cohort Studies – Timing Exposure …